New fossils of “Gyracanthus” sherwoodi Newberry, 1889 are described primarily from the Late Devonian Red Hill site and Metzger's Quarry (Catskill Formation, late Famennian) of Clinton and Sullivan Counties in central Pennsylvania. The fossils include ornamented prepectoral ventral plates, pectoral, pelvic, and dorsal fin spines, elements of the endoskeletal shoulder girdle (procoracoid and scapulocoracoid), scales, and possible anal fin spines. We distinguish between anterior and posterior dorsal fin spines. A growth series of elements, described for the first time for a gyracanth, show that the adults of this taxon reached about a meter in length, and juveniles already had ossified endoskeletal pectoral elements at body lengths 300–400 mm. The mainly cartilaginous skeleton, paired fin spines, shoulder girdle structure, and scale growth are consistent with gyracanthids being stem chondrichthyans. “Gyracanthus” sherwoodi lived in non-marine conditions in the eastern Laurentian rivers and deltas.